This invention relates to a method for the epoxidation of olefins of lower reactivity, such as propylene with a less stable organic hydroperoxide, such as cyclohexyl hydroperoxide in the presence of a molybdenum-containing catalyst to give high hydroperoxide conversions and high yields of epoxide product, by employing a critical amount of a stabilizing agent consisting of a secondary or tertiary monohydric alcohol having from 3 to 9 carbon atoms such as tertiary butyl alcohol.
In recent years an olefin epoxidation process has been developed wherein the olefinic compound is epoxidized utilizing an organic hydroperoxide as the oxidizing agent and a molybdenum-containing catalyst. This process and the catalysts therefor have been widely described in both U.S. and foreign patents. The process and catalysts are described in U.S. Pat. 3,351,635 (1967) and Belgium Pat. No. 674,076, dated June 20, 1966. Additional molybdenum-catalysts for this reaction are described in U.S. Pat. Nos. 3,434,975 (1969); 3,453,218 (1969) and 3,480,563 (1969).
This process gives extremely good conversions and yields when a highly stable hydroperoxide is utilized to epoxidize a reactive olefin. Thus, commercially, tertiary butyl hydroperoxide is used as the oxidizing agent with excellent results. There is one disadvantage of limiting the oxidizing agent solely to tertiary butyl hydroperoxide and that arises since the reduction product is tertiary butyl alcohol and, accordingly, in order to render the process economically feasible, it is necessary to use or sell this by-product as well as the olefin epoxide product.
Various other hydroperoxides less stable than tertiary butyl hydroperoxide have been proposed since their corresponding reduction product, i.e. the alcohol, has potentially greater value as such or as an intermediate in the production of more valuable products. Unfortunately, heretofore, when attempts were made to use these less stable hydroperoxides, for example cyclohexyl hydroperoxide or amylene hydroperoxide, poor conversions and low yields were obtained, particularly when they were used to epoxidize less reactive olefins, such as the alpha-olefins (terminally unsaturated olefins) or olefins with electron withdrawing groups alpha to the double bond, i.e. chloro, hydroxyl and similar groups. An example of such less reactive olefins are the allyl chloro compounds.
It is only when these less stable hydroperoxides are used to epoxidize the highly reactive olefinic compounds such as the internal olefins, i.e. compounds having alkyl groups surrounding the double bond, that desired high conversions and yields are obtained. Thus, even though many of the derivatives from these hydroperoxides would have potentially a high value, they were not used commercially in the epoxidation of propylene to propylene oxide, one of the most useful epoxide compounds, since this compound is an alpha-olefin and thus is less reactive. When their use was attempted it was found that both the conversion of the hydroperoxide and yield of epoxide were poor.
The instant invention provides a method for obviating these difficulties and permits the use of the less stable hydroperoxide as the oxidizing agent in conjunction with a monlybdenum-containing catalyst to epoxidize even the less reactive olefins such as the alpha-olefins and the olefins substituted with an electron withdrawing group on the carbon alpha to the double bond to give excellent hydroperoxide conversion and high yields of the epoxide product. Important examples of such compounds are propylene and allyl chloride or allyl alcohol, respectively. This method employs a critical amount of a stabilizer compound which is a secondary or tertiary monohydric alcohol having from 3 to 9 carbon atoms.